A bearing is a device to allow constrained relative motion between two or more parts and to reduce frictions between the parts. Bearings can be classified broadly according to the motions they allow and according to their principle of operation, as well as by the directions of applied loads they can handle. For example, bearing can be classified into a contact bearing and a non-contact bearing. A contact bearing contacts a rotating object to support the object. A non-contact bearing does not contact a rotating object with a gap between the non-contact bearing and the rotating object, to support the object. However, there is a possibility for the rotating object to move in a radial direction due to the existence of the gap between the non-contact bearing and the rotating object, thereby a balance of the rotating object may be lost.